1. Field of the Invention:
The invention relates to a method for the direct reduction of particulate iron-oxide-containing material in a shaft furnace. Reformed gas from a reformer is fed as reducing gas to a reducing zone of the shaft furnace. The directly reduced ferrous particles are discharged from the shaft furnace and the top gas forming during reduction is extracted from the upper section of the shaft furnace. A hydrocarbon-containing gas is injected into the shaft furnace, and, if desired, the directly reduced ferrous material (sponge iron) is cooled by means of a cooling gas guided in a recirculating system through the shaft furnace.
2. Description of the Related Art:
Methods of this type have been known for long. The directly reduced ferrous material forming has a carbon content that is not sufficient for further processing into steel. Accordingly attempts have been made to increase the carbon content of the ferrous material (sponge iron) by additional measures.
Thus, is has been proposed according to U.S. Pat. No. 4,054,444 to introduce low hydrocarbons, in particular methane, into the shaft furnace below the reducing zone and to provide for a cooling gas recirculating system in the lower section of the shaft furnace so as to promote the release of carbon according to the Boudouard reaction. However, these measures, according to recent findings, are not always successful in adjusting the carbon content desired in the finished product (sponge iron). In particular, because the cracking temperature of methane is very high and back reactions ("methanization") are likely to occur on account of the reactions in the shaft furnace, even under the consumption of carbon.